The present invention relates to a motor pump, and more particularly to a canned motor pump having a circulation system for a treating liquid circulating within a rotor chamber of a canned motor section for cooling the motor section and for lubricating its bearing.
In general, a canned motor pump is, as shown in FIG. 2, essentially comprises a pump section 16 and a canned motor section 22. The pump section 16 includes a casing 10, a main impeller 12 and a liner disc 14. The canned motor section 22 includes a stator assembly 18 and a rotor assembly 20. Both the pump section 16 and the canned motor section 22 are connected by adaptor 24. The main impeller 12 and the rotor assembly 20 are respectively mounted on a rotor shaft 32 which is supported by a liner ring 26, a front bearing 28 and a rear bearing 30.
In such canned motor pumps, the rotor shaft 32 is not sealed. Then, the treating liquid of the canned motor pump serves to cool the motor section 22 and to lubricate the front and rear bearings 28 and 30. With respect to canned motor pumps resistive to a hot treating liquid, the circulation of the treating liquid for cooling the motor section 22 and lubricating the front and rear bearings 28 and 30 are achieved by an auxiliary impeller 38 independent of the main impeller 12. The auxiliary impeller 38 is provided on a side of a front rotor chamber 34 involved in the motor section 22. Thus, the auxiliary impeller 38 serves for making the pressure of the treating liquid rise. Then, the treating liquid is circulated through a pipeline 40, a cooler 42, a pipeline 44, a liquid reservoir 46, a passage 48 and a surface of the rear bearing 30, a rear rotor chamber 36, the front rotor chamber 34, a passage 50 and a surface of the front bearing 28 and thus back to the auxiliary impeller 38. As a result of those, the cooling for the motor section 22 and lubricating for the front and rear bearings 28 and 30 are achieved.
Although such circulation of the treating liquid for cooling and lubricating operations are achieved by the auxiliary impeller 38 independent of the main impeller 12, such circulation system is poor in reliability, especially to a high temperature treating liquid which is likely to be gasified.
In FIG. 3 showing the auxiliary impeller 38 section, the treating liquid in the front rotor chamber 34 is transmitted to a suction inlet port 52 of the auxiliary impeller 38 through the passage 50 and the bearing surface of the front bearing 28. In the auxiliary impeller 38, the pressure of the treating liquid is raised and discharged through a discharging port 54. With respect to the pressure of the treating liquid, since the suction inlet port 52 communicates with a suction inlet port of the main impeller 12 through passage 56 and the liner ring 26 (see FIG. 2), a suction pressure of the treating liquid at the suction inlet port 52 is so set as to be approximately equivalent to a suction pressure of the treating liquid at the main impeller 12, and thus in a main process (hereinafter referred to as a main process suction pressure).
Further, the pressure of the treating liquid in the rotor chamber, particularly in the front rotor chamber 34 directly communicating with the suction inlet port 52 through the passage 50 is also so set as to be approximately equivalent to the suction pressure of the main process. In case that the treating liquid is a high temperature and liable to be gasified, if the treating liquid cooled by the cooler 42 becomes a higher temperature than a predetermined value, the circulating treating liquid is readily gasified. Therefore, the problems with the conventional cooling and lubricating system are that the gasification of the circulating treating liquid prevents the cooling of the motor section and the lubrication of the bearing. Further, the gasification of the circulating treating liquid causes cavitation, erosion and other affections, when bubbles produced by the gasification burst.